<!DOCTYPE html>
<html>
    <head>
        <style>
            .father{
                width: 500px;
                height: 200px;
                position: relative;
                background-color: azure;
                border: solid 1px red;
            }
            .child{
                /* margin: 5px auto ; */
                border: solid 2px;
                position: absolute;
                top:0;
                bottom:0;
                left:0;
                right:0;
                margin: auto;
            }    
        </style>
    </head>
    <body>
        <div class="father">
            <div class="child">
                <p>11111</p>
            </div>
        </div>
    </body>
</html>